We show that output sequences produced by synchronous sequential circuits in response to test sequences that achieve high fault coverage have certain distinct properties.We demonstrate that these properties are useful as part of a property-based (simulation-based)test generation procedure.The importance of these properties is that they provide additional heuristics to drive property-based test generation,which to-date achieves the highest fault coverages reported for benchmark circuits.These additional heuristics are expected to improve the ability of property-based test generation procedures to achieve complete fault coverage in an ef .cient manner.